OBSTACLE AVOIDANCE LEGGED ROBOT.

MOHAMED FAIZAN BIN BASHEER AHMAD

This thesis is submitted as partial fulfillment of the requirement for the

award of the Bachelor Degree of Electrical Engineering (Electronic)

Faculty of Electrical & Electronic Engineering

University Malaysia Pahang

NOVEMBER 2008

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DECLARATION

“All the trademark and copyrights use here in are property of their respective owner.

References of information from other sources are quoted accordingly, otherwise the

information presented in this report is solely work of the author”.

Signature : ________________________________________

Author : MOHAMED FAIZAN BIN BASHEER AHMAD.

Date : 21 NOVEMBER 2008.

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DEDICATION

Specially dedicate to

My beloved parents, brothers and sisters.

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ACKNOWLEDGEMENT

First, I would like to express highest gratitude to my supervisor, Encik Saifudin

b. Razali for the guidance and co-operation that been given throughout the progress and

completion of this project.

I also deeply thank to my family who‟s always giving a motivational support and

show me a guidance to pursue my studies at University Malaysia Pahang. Thanks for

their encouragement, support, love, my brothers, sister and many more.

ALHAMDULILLAH.

Finally, my great appreciation to my dear housemates that given me so many

opinion and encouragement till I don‟t know which one to comprehend, especially Hanis

, Khawarizmi and Mohd Noor thanks for their brilliant idea and my class mate whom

involve directly or indirectly with this project. Last but not least the dedication of a

thousand of thank to dear Hasinah that is a special one to me that had always been a

backbone for me and gave plenty of motivation, moral support and so on. Finally thank

you Allah since through your blessings I managed to do all in time. Thank You very

Much.

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ABSTRACT

Many mobile robots require an operator‟s vision and intelligence for guidance

and navigation. Animals use sensory systems such as hearing, and tactile to move freely

through their environment. The aim of this project is to develop an avoidance behaviors

program for a mobile robot that consists of 8 servo motors that been employed at 4 legs.

Each leg contains 2 servo motors, one for X-axis and one for Y-axis. A PIC

Microcontroller has been implemented to act as a brain for the robot that controls the

walking and turning algorithm. Ultrasonic sensor was also developed to act as an „eye‟

to the system and tells the brain about existence of obstacle in front. As a resultant, the

obstacle avoidance legged robot system is been successfully developed that allows and

will navigate the robot to move through the environment freely. But there is a certain

limitation for the robot such as the wideness of the area, type of obstacle and surface.

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ABSTRAK

Di dalam dunia permodenan dan kontemporari seperti ini robot memerlukan

operator dan kebijaksanaan wawasan untuk tujuan panduan hala tujunya. Demikian

adalah cara yang digunakan haiwan iaitu sistem-sistem deria pendengaran, dan sentuhan

untuk bergerak dengan lebih bebas menerusi alam sekitar mereka. Matlamat projek ini

adalah untuk membangunkan satu pergerakan pengelakan atur cara untuk satu

kepergerakan robot yang mengandungi 8 servo motor yang berfungsi di setiap kaki.

Keseluruhan robot itu mempunyai 4 kaki dan pada tiap kaki mengandungi 2 servo motor

, satu untuk pergerakkan paksi X dan satu lagi untuk pergerakkan paksi Y. Satu PIC

Microcontroller telah digunakan dan ia berfungsi sebagai satu otak untuk mengawal

robot itu dengan wujudnya algoritma berjalan dan algoritma selekoh. Deria ultrasonik

juga dibuat supaya ia berfungsi sebagai satu 'mata' bagi robot itu.

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TABLE OF CONTENT

Title Page i

Declaration ii

Dedication iii

Acknowledgement iv

Abstract v

Abstrak vi

Table of Contents vii

List of Chapter viii

List of Table xi

List of Figures xii

List of Symbol xiv

List of Appendices xv

viii

LIST OF CHAPTER

CHAPTERS TITLE PAGES

1 INTRODUCTION

1.1 Overview 1

1.2 Objective of the Project. 2

1.3 Scope of Project. 2

1.4 Outline of Thesis. 3

2 THEORY AND LITERATURE REVIEW

2.1 Introduction. 4

2.2 Servo Motors. 4

2.2.1 Pulse Width Modulation for Servo. 7

2.2.2 Inside Servo. 8

2.3 PIC Microcontroller. 9

2.4 Robotics. 14

2.4.1 Robot Component. 15

2.4.2 Robot Kinematics: Position Analysis 16

2.4.3 Denavit-Hartenberg Representation 18

2.5 Sensors. 21

2.5.1 Proximity Sensors. 23

2.5.2 Optical Proximity Sensors. 23

2.5.3 Infrared Sensors. 24

2.5.4 Ultrasonic Proximity Sensors. 25

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3 SYSTEM DESIGN

3.1 Introduction. 27

3.2 Hardware Implementation. 29

3.2.1 Power Supply Module. 29

3.2.2 PIC Micrcontroller. 30

3.2.3.1 PIC. 31

3.2.3.1 Oscillator and Reset. 32

3.2.3.1 Programmer. 33

3.2.3.1 LED Connection. 34

3.2.4 Servo Motor. 35

3.2.5 Ultrasonic Sensor. 37

3.2.6 The Robot Movement Design. 41

3.2.6.1 Walking Algorithm. 42

3.2.6.2 Turning Algorithm. 45

3.3 Software Implementation. 47

3.3.1 Algorithm and Programming. 47

3.3.2 Processing Explanation of Main Program. 48

3.3.2.1 Initialize. 49

3.3.2.2 PWM Generation. 50

3.3.2.3 Analog to Digital Converter. 52

3.3.2.4 Sensor Detection. 53

4 RESULT AND ANALYSIS.

4.1 Introduction. 55

4.2 Total Result Robot Algorithm. 56

4.3 Mathematical Expression of the Leg. 60

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5 CONCLUTION AND RECOMMENDATION.

5.1 Conclusion. 63

5.2 Problem and Solution. 64

5.3 Recommendation. 65

5.4 Costing and Commercialization 66

REFERENCE 68

xi

LIST OF TABLES

TABLES NO. TITLE PAGES

2.0 Hitec HS-322HD servo motor specification. 6

2.1 The advantages and disadvantages of robots. 14

2.2 Elements of robots. 15

2.3 D-H parameters table. 20

2.4 Sensor characteristic that need to be consider. 22

3.0 Port connection to the leg. 36

4.0 The robot leg D-H parameters table. 61

5.0 Costing of the project. 66

xii

LIST OF FIGURES.

FIGURES TITLE PAGES

2.0 Wires for the servo motor. 5

2.1 Servo motor Hitec HS -322HD dimension. 5

2.2 Position of motor shaft. 7

2.3 The inner part of servos. 8

2.4 Clock/instruction Cycle. 11

2.5 Pin diagram. 12

2.6 A D-H representation for joint link combination. 18

2.7 Optical proximity sensors 24

2.8 IR sensor reflections 25

2.9 Schematic ultrasonic sensors 26

3.0 Flow chart of the robot system. 28

3.1 Picture of the robot. 28

3.2 LM7805 regulator. 29

3.3 Schematic circuit of +5V power supply. 30

3.4 Pin configuration for PIC16F877A. 31

3.5 Oscillator circuit. 32

3.6 USB ICSP PIC PROGRAMMER. 33

3.7 Connection at main development board. 33

3.8 LED connections at PortB. 34

3.9 Position of the servo motor in the leg. 35

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3.10 Circuit Configuration for all 8 Servo Motor. 36

3.11 Ultrasonic sensor at the quadruped robot. 37

3.12 The circuit design for ultrasonic. 38

3.13 Transmitter circuit. 38

3.14 Receiver circuit. 39

3.15 Frog Movement. 41

3.16 The movement style for robot walking straight. 42

3.17 The movement style for robot walking straight (cont). 43

3.18 The movement style for robot walking straight (cont). 44

3.19 The movement style for robot to turn left. 45

3.20 The movement style for robot to turn left (cont). 46

3.21 General flow chart of program. 48

3.22 Name and variable. 49

3.23 Example pulse generation. 51

3.24 ADC application in the main program 52

3.25 Walking and the sensing flow chart. 54

4.0 Result robot walk straight. 57

4.1 Result of turning left after detection of the obstacle. 58

4.2 Result of turning left after detection of the obstacle (cont). 59

4.3 Leg represent in robotic analysis. 60

xiv

LIST OF SYMBOL.

ms - Millisecond.

I/O - Input Output.

IC - Integrated Circuit.

R - Resistor.

C - Capacitor.

Cθ - cos (θ)

Sθ - sin (θ)

LED - Light Emitter Diode.

IR - Infrared.

k - Kilogram.

V - Voltage.

mA - mili ampere.

kg - kilo gram.

PWM - Pulse Width Modulation

ADC - Analog Digital Converter

PIC - Programmable Interface Controller

xv

LIST OF APPENDICES.

APPENDIX TITLE PAGE

A SOFTWARE DEVELOPMENT 69

B MICROCHIP PIC16F877A DATA SHEET. 78

LM7805 DATA SHEET. 81

HITEC HD-322HD DATA SHEET. 82

CHAPTER 1

INTRODUCTION

1.1 OVERVIEW.

Robots are designed to be controlled by a controller, computer or similar devices.

Basically mobile robots require an operator’s vision and intelligence for guidance and

navigation. The movement for the robot itself has many methods such as wheels, legs

and many more. This movement method is to ensure the smoothness of moving in

different type of surfaces.

A simple wheeled vehicle is easy in mechanical design, controlling, and the

construction part. But it doesn’t work efficiently in all kind of surface. On a rough

terrain, it performs poorly. The radius of a wheel could pass only a certain height of

obstacle. To pass most of the obstacle that it meets, larger wheel radius need to be

designed. However, this approach is impractical in many cases.

On the other side, legged robots are more capable of moving across rough

terrain. That’s why the legged locomotion became a research of interest. But the legged

robots are much more challenging to control compared wheel robots. Each leg consists

of at least two motors. Controlling the one motor for left and right and another motor for

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up and down is difficult. An algorithm for walking must be developed in order the robot

to walk. As a result, legged robots movement must be carefully studied and be

controlled in such way so that it could stand and walk in a stable fashion.

1.2 OBJECTIVE OF THE PROJECT.

The aim of this project is to develop an avoidance behaviors program for a

mobile robot that consists of 4 legs that employs 8 servo motors. A PIC Microcontroller

is been implemented to act as the brain for the robot that controls the walking and

turning algorithm. The system and the programming will be able to control the

movement of the legged so the robot able to walk straight ahead, make left turns and

avoid obstacle.

1.3 SCOPE OF PROJECT.

Several scopes have been outlined to achieve this project. Scope of this project

includes developing a program using high level language PIC Basic Pro for the

PIC16F877A microcontroller, constructing the hardware module for it, attachment of

servo motors and integration of ultrasonic sensor with the microcontroller. Developing

an algorithm program for the robot to walk ahead, make a left turn and is capable to

avoid obstacle.

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1.4 OUTLINE OF THESIS.

This thesis consists of five chapters. This chapter is discussed about the

background of robot, the objective, and scope of the project. In chapter 2 is more

towards reviewing about literature study. It discusses about the function of the servo

motor and it could be operated using PWM, about details of PIC16F877A

microcontroller, about other robotic research that been done and about various type of

sensor. In chapter 3 is been discussed about methodology for hardware and software

implementation into the project. The result, analysis and discussion will be on the

chapter 4. Finally, chapter 5 discusses the conclusion of the project and future work that

can be done to improvise this project.

CHAPTER 2

THEORY AND LITERATURE REVIEW

2.1 INTRODUCTION.

This chapter is upon the study on servo motor, PIC microcontroller, robots

analysis and sensors. Servo motor was reviewed upon controlling it using PWM and

how it could be used as a device that controls a degree of freedom in a quadruped robot.

The PIC microcontroller discussed more towards the capability of it and thorough detail

on the functions and the operations of it. Type of sensors compared in this chapter.

2.2 SERVO MOTORS.

Servo motors are commonly used in robotics especially that uses leg for

movement purpose for the robot. This was because they are light-weighted, compact and

durable. Since their control and power electronics were all built-in, interfacing hardware

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requirement is much simplified. Compared to toy motors, the torque of servo motors are

high so the servo motors better suited to robot development.

Each servo motor has three wires, that is yellow, red and black. As shown in

Figure 2.0 red is for power, black is for ground, and yellow is for pulse-width

modulation (PWM) pulsing. This pulsing controls the position which the shaft of a servo

motor should rotate.

Figure 2.0: Wires for the servo motor, black (ground), red (power), yellow (PWM)

Figure 2.1 shows the servo motor dimension that been used in this project, the

servo motor that been used is Hitec HS -322HD servo motor. The specification of the

servo is show in Table 2.0.

Figure 2.1: Servo motor Hitec HS -322HD dimension. (The dimension in mm)

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Table 2.0: Hitec HS-322HD servo motor specification [1].

Operating voltage range 4.8V to 6V

Test Voltage 4.8V 6V

Operating speed 0.19s/ 60° at no load 0.15s/ 60° at no load

Stall Torque 3kg. cm 3.7kg. cm

Ideal current at stopped 7.4mA 7.7mA

Running current 160mA/ 60° at no load 180mA/ 60° at no load

Stall current 700mA 800mA

Motor type Cored metal brush

Potentiometer type 4 slide/ direct drive

Amplifier type Analog controller and transistor drive.

Dimension 40 x 20 x 36.5mm

Weight 43g

Ball bearing Top/ Resin bushing

Gear material 2 heavy duty resin

Horn gear spline 24 segments

Connector wire length 300mm

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2.2.1 PULSE WIDTH MODULATION FOR SERVO

Pulse-width modulated (PWM) signal is a train of pulses with varying width.

Each servo motor does have its own unique pulsing width. But these listed

configurations are for the servos that have been used in this project that is HS-322HD.

The full duty cycle or called period for a whole pulsing must be 20ms. Figure 2.2, shows

the movement of the degree upon the timeline (PWM) of the duty cycle produced. The

time of 0.6ms, 1.5ms and 2.4 ms signaled the motor shaft to turn to 0 degree, 90 degrees

and 180 degrees respectively. The motor shaft could not go any further than below 0

degree and above 180 degree range unless modifications were made to the servo motor.

Figure 2.2: Position of motor shaft when PWM is generated.

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2.2.2 INSIDE SERVO

The servo motor has some control circuits and a potentiometer (a variable

resistor, a.k.a. pot) that is connected to the output shaft. In the Figure 2.3, the pot can be

seen on the right side of the circuit board. This pot allows the control circuitry to

monitor the current angle of the servo motor. If the shaft is at the correct angle, then the

motor shuts off. If the circuit finds that the angle is not correct, it will turn the motor the

correct direction until the angle is correct. A normal servo is used to control an angular

motion of between 0 and 180 degrees. A normal servo is mechanically not capable of

turning any farther due to a mechanical stop built on to the main output gear.

Figure 2.3: The inner part of servos.

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2.3 PIC MICROCONTROLLER

For this project, the controller is used as a brain for the whole system. From the

input from sensor until the output for the servo motor is controlled totally using this PIC

microcontroller. Describing about the PIC microcontroller and in the mean time will be

given more understanding upon employing this controller. Almost all type of PIC

microcontroller is included in a class of 8-bit microcontrollers of RISC architecture.

Basically, the PIC architecture is minimized to be a simpler item but it still operates at

the same function. The Harvard architecture is a newer concept than von-Neumann. It

was designed as a response for the need to speed up the work of a microcontroller. In

Harvard architecture, data bus and address bus are separate. Thus, the data will flow

directly through the central processing unit and the address bus is neglected. This greater

flow of data will impact for a greater speed of work. Besides that, the architecture will

involve for a small number of a fixed length instruction. It means the instruction is not to

have to be 8-bit words but it can uses 14 bits for instructions which allows for all

instruction to be one word instructions. Microcontrollers with Harvard architecture are

called "RISC microcontrollers". RISC is a short form for Reduced Instruction Set

Computer. Microcontrollers with von-Neumann's architecture are called 'CISC

microcontrollers'. CISC is a short form for Complex Instruction Set Computer. Same as

discussion before, RISC microcontroller has a reduced set of instructions, maybe 35

instructions for one cycle. If we compared it with Intel’s and Motorola’s

microcontroller, it has over hundred instructions. As a simplified point, we can say that

the features of PIC microcontroller are:

(i) Separate code and data spaces (Harvard architecture).

(ii) A small number of fixed length instructions.

(iii) Most instructions are single cycle execution (4 clock cycles), with single

delay cycles upon branches and skips.

(iv) All RAM locations function as registers as both source and/or destination of

math and other functions.

(v) A hardware stack for storing return addresses.